When iron sulfides in a coal mine are exposed to water containing oxygen and sulfur-oxidizing bacteria, oxidation takes place, which results in the formation of sulfuric acid. The acid mine water so formed constitutes a formidable water-pollution problem that seriously affects the thousands of miles of streams and surface acreage in the United States. In 1972, more than 4 million tons per year of sulfur acids were estimated to have drained from active and abandoned coal mines. The additional strip-mining for coal brought about by the energy crisis could result in even more serious pollution problems. In addition, many streams and rivers are polluted by acid effluents from manufacturing processes. If the pH of such rivers falls below about 5-6, these rivers are no longer able to support marine life. It has been previously suggested that since acid strip-mine lakes take a long time to recover naturally, an energy-source material for the bacteria in the lakes is needed in order to hasten lake recovery and the reestablishment of essentially neutral water. The addition of sewage sludge into an acid strip-mine lake increases the rate of recovery of the lake. The rate of recovery of an acid strip-mine lake can be greatly increased using the biochemical fuel cell principle by the addition of electrodes and a simple external circuit in the lake. In addition, it may be possible to obtain a modest amount of electrical power for plant operation, a practical means of disposal of sewage sludge, and recovery of some free sulfur.
A basic biochemical fuel cell is described in Sisler U.S. Pat. No. 3,477,879.